Line a large baking sheet with foil. Spray lightly with cooking spray.

Place popcorn into a large ziploc bag and crush with a rolling pin.

Combine sugar, syrup, and water in a medium saucepan over medium heat. Cook 1 minute or until sugar dissolves, stirring constantly. Cook, without stirring, until candy thermometer registers 270° (about 8-10 minutes). Stir in molasses and butter; cook until thermometer registers 290° (about 5 minutes). Stir in baking soda, vanilla, and salt. This will bubble rapidly so be careful. Quickly stir popcorn into boiling syrup mixture. Pour popcorn mixture onto prepared pan quickly, but being careful as it is very hot. Spread to 1/4" thickness using a wooden spoon coated with cooking spray. Place on a rack and let cool completely before breaking into pieces.